diff --git a/include/sparsemap.h b/include/sparsemap.h
index 641dca2..f2ac2c7 100644
--- a/include/sparsemap.h
+++ b/include/sparsemap.h
@@ -263,8 +263,8 @@ void sparsemap_scan(sparsemap_t *map, void (*scanner)(sm_idx_t vec[], size_t n,
  *
  * @param[in] map The sparsemap reference.
  * @param[in] other The bitmap to merge into \b map.
- * @returns 0 on success, -1 and sets errno to ENOSPC when the merge might
- * require more space than available.
+ * @returns 0 on success, or sets errno to ENOSPC and returns the amount of
+ * additional space required to successfully merge the maps.
  */
 int sparsemap_merge(sparsemap_t *map, sparsemap_t *other);
 
diff --git a/src/sparsemap.c b/src/sparsemap.c
index 0520da9..b423bdc 100644
--- a/src/sparsemap.c
+++ b/src/sparsemap.c
@@ -975,6 +975,19 @@ sparsemap(size_t size)
   return map;
 }
 
+sparsemap_t *
+sparsemap_copy(sparsemap_t *other)
+{
+  size_t cap = sparsemap_get_capacity(other);
+  sparsemap_t *map = sparsemap(cap);
+  if (map) {
+    map->m_capacity = other->m_capacity;
+    map->m_data_used = other->m_data_used;
+    memcpy(map->m_data, other->m_data, cap);
+  }
+  return map;
+}
+
 sparsemap_t *
 sparsemap_wrap(uint8_t *data, size_t size)
 {
@@ -1273,11 +1286,12 @@ sparsemap_merge(sparsemap_t *map, sparsemap_t *other)
   size_t src_count = __sm_get_chunk_map_count(other);
   size_t dst_count = __sm_get_chunk_map_count(map);
   size_t max_chunk_count = src_count + dst_count;
+  ssize_t difference = map->m_capacity - (other->m_data_used + src_count * (sizeof(sm_idx_t) + sizeof(sm_bitvec_t) * 2));
 
   /* Estimate worst-case overhead required for merge. */
-  if (map->m_data_used + src_count * (sizeof(sm_idx_t) + sizeof(sm_bitvec_t) * 2) > map->m_capacity) {
+  if (difference <= 0) {
     errno = ENOSPC;
-    return -1;
+    return -difference;
   }
 
   dst = __sm_get_chunk_map_data(map, 0);